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Calculation of activity duration ???????????????

16 replies [Last post]
Andrew Dick
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While doing some analysis of our construction program, I have drawn the following conclusion;

I’m Confused…….

I have 1 activity on a 9 hr/day calendar (7:30 – 4:30), 10 days in duration. The activity starts at 0730 on the first day and finishes at 15:30 on the 9th day. This is some 1 day 1 hour early.

What I reckon is that we say we are able to work for 9 hours each day and the system default is 8 hrs per time period.

Therefore the planned 10 days * 9H/d = 90Hrs duration is calculated at 8H/d for 10 days based on a 9hr/d calendar therefore giving an early finish equal to 10 hours early. I.E 9th day at 15:30Hrs.

Now how do you reckon this will extrapolate over a 2 year construction program that is working on a construction calendar equal to 7 days/week 9 hrs/day when as far as Primavera is concerned all durations and therefore end date is calculated based on 8Hr/d, 40Hr/W, 172Hr/M, 2000Hr/Y. When what we’re saying is we need 9H/d, 63H/w, 273H/m, and 3276H/y less Easter and xmas break.

Has anybody else confirmed this??

How do I fix it??

Have I grabbed hold of the right end of the bull??

I don’t have access to the global admin settings.



Mike Testro
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Gooday Andrew

Sorry to say it me old mukker.

Switch to PowerProject and solve all your problems.

Best regards

Mike T.
Paul Naughton
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P5/6 calculates in hours but can report in just about anything. If you are working in days and update a duration to ’5’ the systems calculates this in hours (5* global day value e.g. 8hrs = 40 hours) it then spreads these hours over the calender for that activity so for this example on a 10hr calenday you will be finished in 4 days.

If you are working with multiple calenders changing the global value will just move the problem. You do have the option of enterning the duration in hours when displaying values in days, in this example adding ’50h’ would give you a ducation that covers 5 days rather than 4. Not always practical but does solve the problem. Hope this makes sense.

This also explains why float readings sometimes appear all over the place.
Tony Scott
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I’ve run into this issue being discussed here a couple of times on this project. We have a multitude of calendars as our project will be taking place in different areas with different weather conditions, and have many aspects that can only happen at certain times of year. Unfortunately, with the design of P5/6 I’m running into lots of issues.

Going to a purly hourly unit isn’t practical (we’re looking at about an eight year long project, with some long durations on the owner side for control and management schedules).

While P3 had limitations, at lest you could trust it!

Andrew Dick
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Posts: 295
So today I came up with a set of guidelines or benchmark settings that I have shown to a few people.

These settings are designed to provide consistency across the enterprise database with respect to the selection of the units/time period and the global default calendar, and also provide guidance on resource calendar and float calculation,

I beleive my research has shown ALL of these things are interconnected by the units/time period and the global calendar setting, along with a couple of other things.

If anyone would like to provide a review of this proposal please e-mail me at ’’ and I shall send it on.

Nar Thap
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Of course different work hours per day calanders conflict when one is working with day as planning unit. Hourly planning unit will solve this problem however the long durations of days or weeks in hours are much confusing ones.
Se de Leon
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Hi Raviraj,

It’s not also possible to do that in MSP.

In MSP, assignment of working hours for each day in a specific calendar is possible. But nonetheless, same as in P5/P6, days,weeks,months is calculated globally using only 1 and only 1 default value for days,weeks or months i.e. 8 hours per day, 5 days per week or 24 days per month.


This would be an excellent enhancement for P6 or even MSP if the default values for calculating no. of days is day specific. Ex. hours per day assigned to Mar 28, 2008 is 8 hours, while Mar 29, 2008 is assigned 10 hours per day, March 30, 6 hours per day etc.


User offline. Last seen 9 weeks 4 days ago. Offline
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This problem is similar to what we have been asking from years now regarding ramadan working hours.

In GCC countries, construction workers work only for 4 hours a day. So, if u hav planning unit as day, then how to reduce the working hours during that one month of ramadan.

For me, this cannot be done in P3. Thats possible in MSP, I believe.

Does it make sense, or what i am saying is something else? Plz correct me or if u hav solution, plz let me know.


Dennis Hanks
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In a recent risk analysis exercise, I had a similar experience. We had six different schedules with 6 different calendars that we needed to combine into a single project schedule.

The dates calculated correctly, but the durations were all wrong - none of the calendars were the standand 5/40.

This was true in PertMaster too, with an other wrinkle dealing with themes. The workaround was to do everything in hours.

Primavera is working on an ’enhancement’, but IMHO neither product should have been released with this malfunction (bug)
Anoon Iimos
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I’m not sure if this will help you, i got similar situation in P6, i got two different calendars: one 6 days/week (10 hrs/day) and one 5 days/week (8 hrs/day). My time period settings was set to 10 hrs/day work.

When running the schedule (F9), the activity durations came out seems impossible. What I did was changed the 8 hr/day work (in the 5 days/week calendar) into 10 hrs/day to be consistent with the time period settings and running the schedule again seems to give the correct number of days consistent with the duration. It’s quite confusing sometimes, i mean how can you tailor your works to the resource availability? I’m not really sure though...
Andrew Dick
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Thanks for that, I have tried all of your reccomendations, however I think the issue goes deeper than that.

From what I found today, I’ve either lost the plot myself or there is something wrong with the basic settings of Primavera.

I do hope that someone can tell me I’ve lost the plot, as I can probably get medication for that.

Ian Mackrell
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Hi Andrew.

Forgive me if you have tried this. But it sounds like either:

1. Default setting in the calender for 1 hr lunch. You can change this in global changes (i think - don’t have P5 at the moment but have used it). I am aware you can edit your calender per 1/2 hrs.

2. There is a conflict in calenders. I was speaking to someone who has had this problem before. Check all user preferences for anything resembling hrs per day. If one reads 9hrs and another reads 8hrs, then your working day could be 8/9ths of 8 hrs not 9 hrs, which would reduce it even more.

Andrew Dick
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I’ve done some more investigating on this thing that I’m trying to understand.

If anybody would like to have a look at the excel sheet Ive done up to try and better describe my question just drop me a line at

I’ll send you the sheet and would really like to be set straight if I’m on the wrong track.

Andrew Dick
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It seems that the admin setting for units per time period are multiplied by the original duration in days of the activity, then the calculated duration of the activity is a resultant of the lenth of time taken to burn the hours calculated initially against the activity calendar working time.

So what I want is an activity which has a 9 hr day 7 day week calendar to calculate as taking 63 hours over seven days to complete, but what I get is an activity with a 9 hr day 7 day week calendar which only has 56 hours to burn against that calendar - therefore taking 6 days and 2 hours to complete (7 hours short of when I want it to)

Then what you get is the next activity on the critical path scheduling 7 hours early.

Oh dear - What to do??

Andrew Dick
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I’m using P5 SP4.

I have no resources in the schedule and the fault has been replicated on other systems by others.

The admin preferences will not be able to be changed as this will effect the entire database (as you would expect).

This is a major fault with the system as far as I can see, as any calendar you apply to activities in this manner will be over-ridden by the admin preference, and subsequently change the durations to suit the default hours per time period.

I’m still trying to work out the impact to the schedule for when I change the calendar back to an 8 hour day. I think I need to do this to understand the real duration of the construction schedule.

Then I shall need to work out the impacts to the resources when I apply them to see if we go back to the 9 hour calendar, but that will raise a question on the default units/time for the resources.

Fair dinkum if this keeps up I reckon I’ll just use excel.

At least I could trust the answers I get.
Anoon Iimos
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yes, or the admin preference / time period; and also your activity calendars and resource calendars (task dependent, resource dependent), if you got P3, i suggest you counter check the schedule in it
niles luo
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Maybe you should do in the function menu: Edit/User preferences/Time Units/Hours per Time Period. If you can not aceess this function, maybe you can ask your system administrator to give your this privilege.
Good luck